The invention relates to a fastening means for fixing seismic devices of circular shape, especially seismic energy sources airguns, for example, in a defined manner, and especially intended for fixing at least two devices firmly at a mutual distance in a frame structure.
In seismic surveys at sea an array of different seismic devices is towed in the water. In part, such devices are sensitive as regards impact or shock loads, and in part, the towing system proper is sensitive to such loads. Special problems arise in connection with suspending such seismic acoustic sources, e.g. airguns, which are towed in arrays behind the seismic vessel, since they are suspended from below raft arrangements, and the like. Due to the shock and impact loads triggered when the guns are fired, tugs and wear will result both in the air conduits extending to the guns, and in electric control lines, as well as in suspension members. Furthermore, wear and undesirable effects will also arise due to movement of the water, i.e. waves as well as general movement due to towing. Such problems will occur both with separately suspended guns and with guns suspended in framelike devices, in so called clusters.
In an article in the magazine Geophysics, Vol. 44, No. 5 (May 1979), pp 865-879 assembling of airguns in a group or a "cluster" is described, where the guns are attached to the frame at predetermined mutual distances, so that they may be fired while in a constant geometrical arrangement and without said geometrical arrangement being changed by or after firing. Such mounting of airguns in a frame structure results in a number of advantages in seismic surveys, but this technique was known for a long time and does not form any part of the present invention.
In U.S. Pat. No. 4,719,987 (corresponding to Norwegian Patent Application No. 85 2459) another design is shown with seismic sources of energy suspended in groups, where the sources of energy are maintained at a predetermined mutual distance by the aid of a chain means which is attached to the sources by the aid of sleeves. Neither of the above-mentioned publications, however, discloses the mounting of the seismic energy sources in detail.
The mounting proper of such sensitive seismic equipment, however, proved to be critical and decisive to the results achieved during survey, as shock and impact effects may cause distortion of signals, and in case of a group arrangement of airguns in frame structures or chain constellations mutual distances may be changed so that the desired results may not be achieved.